1. Field of Invention
The present invention relates to high intensity light sources and in particular to high intensity light sources which utilise an electric discharge to generate light.
2. Description of Related Art
There are many applications in which high intensity light sources are required. For example, as optical pumps for lasers, e.g. dye lasers, UV light sources in for example UV sterilisation and UV polymer curing, and in the generation of ozone for sterilisation, bleaching etc.
It is an object of the present invention to provide a new and improved form of high intensity light source which utilises an electric discharge to generate light.
According to a first aspect of a present invention there is provided a high intensity light source comprising:
a solid dielectric sheet having a front and a back surface;
a conducting medium in contact with at least a portion of said back surface of the dielectric sheet, said conducting medium being electrically connected in use to a fixed potential;
means for establishing electric charge of a first polarity which is electrostatically bound to said front surface of the dielectric sheet at a potential which is different to said fixed potential; and
selectively-operable means coupled to said front surface of the dielectric sheet for applying a rapid potential change to at least a localised region of said front surface so as to cause the charge built-up on the dielectric sheet to form an electric discharge with the consequential emission of light.
Preferably the means for generating the electrical discharge rapidly applies a voltage to the front surface of the dielectric sheet which voltage is of a polarity opposite to said first polarity. However, it is to be noted that polarity reversal it not essential.
The means for rapidly applying the voltage change to the dielectric sheet may be application of ground (earth) potential or it may be a pulse generating means. The electrical pulse generating means may comprise a high voltage pulse generator coupled to the front surface of the dielectric sheet by an electrical conductor. Typically, the pulse generating means is arranged to generate a pulse having a voltage of between 5 V and 30 KV, for example approximately 20 KV. Alternatively however, the pulse generating means may be a step voltage generator or an impulse voltage generator.
The means for establishing the electrical charge may comprise a thermionic emitter, a field emitter, an electron beam or an ion beam generator or a Corona discharge generator.
The dielectric sheet may be sufficiently thin as to be flexible or may be relatively thick and rigid and may be made of, for example, nylon, polyester, polyethylene, PTFE, PVC, rubber, glass, quartz, ceramics or oil-impregnated paper. The dielectric sheet may also be such that said electrical discharge is wholly or partially located within the dielectric sheet, close to the front surface. The dielectric sheet may be photoconductive to achieve a more rapid discharge due to the increase in conductivity when discharge occurs.
Said conducting medium is preferably a solid conducting medium evaporated, adhered to, or otherwise contacting said back surface of the dielectric sheet. The conducting medium may be a metal, a semiconductor, a photoconductor, or a conducting polymer. When the conducting medium is a photoconductor it may be possible actively and transiently to write a conducting pattern onto the conducting medium, e.g. using a laser, to control the path of the electrical discharge. The solid conducting medium may have any appropriate shape. For example, the conducting medium may comprise one or more wires or tracks arranged in parallel, in spokes, or in a spiral.
Alternatively, the conducting medium may be a conducting plasma exposed to the back surface of the dielectric sheet.
The dielectric sheet and the conducting medium of the high intensity light source may be contained within a sealed housing within which said electrical discharge is generated. The housing may be evacuated or may contain a gas such as air, neon, xenon, argon, helium, mercury vapour, carbon dioxide, SF6 or any combination of these whereby by appropriate selection of the atmosphere the emission spectrum of the light source may be varied or tuned through the range covering infra-red, visible and ultraviolet.
Preferably, said charge is built-up on the front surface of the dielectric sheet by exposure to an electrical discharge. Preferably, a unipolar Corona discharge. The means for generating the Corona discharge may comprise a multiplicity of Corona electrode points or wires disposed in front of the front surface of the dielectric sheet. The Corona voltage may be in the range of 20 v to 50 KV, for example approximately 40 KV.
The dielectric sheet may have any suitable shape and, if flexible, it may be reconfigurable. For example, the dielectric sheet may be substantially planar. Alternatively, the sheet may be cylindrical, part-spherical, conical, or parabolic. It will be appreciated that, providing that the surface exposed to the electrical discharge is on the inner surface of the dielectric sheet, these arrangements can be used to concentrate light in a particular direction.
By virtue of the present invention, which utilises only a small amount of energy to initiate the discharge and a separate mechanism for building up and storing charge on the dielectric sheet, the conversion efficiency of the light source is high and the discharge path length need not be curtailed. Furthermore in particular embodiments the emission spectrum is tunable and if the dielectric sheet is flexible the source may be geometrically reconfigured to direct the light emission in a preferred direction. The source can be made relatively small and portable whilst delivering high intensity light to a closely-coupled target.
According to a second aspect of the present invention there is provided a method of generating light pulses using a light source comprising a dielectric having a front and a back surface and a conducting medium in contact with at least a portion of said back surface of the dielectric sheet, the method comprising the steps of:
applying a fixed electrical potential to said conducting medium;
causing a build up of charge to occur on the front surface of the dielectric sheet; and
subsequently applying an electrical voltage pulse to the front surface of the dielectric sheet to discharge the built-up charge.